The degradative attack of a metal by its environment through chemical or electrochemical means is a description of the corrosive process. The literature deals extensively with agents that retard corrosion of metal surfaces. Using iron as a representative metal, corrosion has been viewed to occur at sites consisting of electromotive cells. The anode region converts iron to iron (II) with electron liberation. To maintain electrical neutrality, the cathode region finds protons (hydronium ions) capturing electrons evolving hydrogen under acid conditions or oxygen reduced to hydroxide in the presence of water under alkaline or neutral conditions. The ferrous hydroxide produced from the coupled electrochemical reaction is subsequently oxidized to ferric oxide, rust, which due to its larger expansion by comparison to iron metal ruptures and fails to form a protective layer on the iron surface.
Agents that interfere with any of the above critical steps in the corrosion cycle act as inhibitors. The present invention will describe novel compounds that contain two structural features acting in concert to control corrosion. The first is an alkoxy silane that can form a passivating multidimensional cohesive film barrier capable of adhesive covalent bonding to the surface of many metals in the presence of moisture. The second is a carbon bound substitutent on the silicon center of the alkoxy silane, immobilized in molecular proximity to the metal surface by the above described bonding and designed to act as either a resistive/hydrophobic, pH control, ion immobilizing or free radical inhibiting center. The examples below demonstrate the synthesis of these materials and their corrosive reducing properties when applied to iron surfaces in a prescribed manner.
The use of silanes to inhibit corrosion of iron or steel is not broadly new. Representative examples of prior disclosures include U.S. Pat. No. 3,890,269 to Martin teaches the preparation of aminofunctional organopolysiloxanes which are said to be useful as sizing agents and as corrosion inhibitors. U.S. Pat. No. 3,759,751 discloses a wash primer comprising an epoxy resin, an inorganic chromate, and an aminosilane for use on aircraft surfaces. British Pat. No. 1,409,483 discloses methylaminoethyltriethoxysilane as a corrosion inhibitor for nonferrous metals and alloys. U.S. Pat. No. 4,310,575 to Khayat discloses trimethylsilylacetamide as a corrosion inhibitor for steel. The present invention provides novel silane compounds which have utility as corrosion inhibitors for metal surfaces.